Compact sensor module

ABSTRACT

A compact sensor module and methods for forming the same are disclosed herein. In some embodiments, a sensor die is mounted on a sensor substrate. A processor die can be mounted on a flexible processor substrate. In some arrangements, a thermally insulating stiffener can be disposed between the sensor substrate and the flexible processor substrate. At least one end portion of the flexible processor substrate can be bent around an edge of the stiffener to electrically couple to the sensor substrate

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/405,594, filed Feb. 27, 2012, and entitled “COMPACT SENSOR MODULE,”the contents of which are incorporated by reference herein in theirentirety and for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention relates generally to a sensor moduleincluding a sensor and processing electronics.

2. Description of the Related Art

Sensor modules that include both a sensor and a processor (e.g., ageneral purpose processor or an Application-Specific Integrated Circuit,or ASIC) can be useful in a variety of optical, electrical, andelectronic applications. In some implementations, it can be desirable toarrange the sensor module so that the sensor and processor arepositioned relatively close to one another. For example, analog signalscan experience parasitic losses as the signals are transmitted over adistance, which can degrade the accuracy and quality of the detectedsignal. Positioning the sensor near the processor can reduce oreliminate parasitic losses associated with signal transmission betweenthe sensor and the processor. The processor can then perform variouspreconditioning and/or preprocessing operations, such as convertinganalog signals to digital signals, within the sensor module. Theprocessor can transmit the processed digital signals to an externalcontrol module, which can be located far from the sensor, with minimalor no parasitic transmission losses to the signals.

One problem associated with positioning the processor near the sensor isthat the heat generated by the processor may be transmitted to thesensor or the sensor substrate. It can be undesirable to transmit heatto the sensor for a variety of reasons. For example, the heat can causedamage due to a mismatch of the thermal coefficients among the parts.Heating the sensor can also be undesirable by inducing increasedtemperatures on the sensor that can damage sensor components or that caninterfere with the signals detected by the sensor. Therefore, while itcan be advantageous to position the processor near the sensor to improvethe quality of the signals detected and transmitted from the sensor, itis also important in some implementations to prevent the sensor fromoverheating due to operation of the nearby processor.

Another consideration when designing sensor modules is ensuring that thesensor module (e.g., including the sensor and the processor) is compactor small enough to comply with the overall system design requirements,which can be important whether the modules are employed individually orare assembled in an array. For example, in some arrangements, an arrayof sensor modules is used to detect signals received in variouslocations or at different angles. In some applications, an array ofsensor modules can be used for imaging applications, such as for x-raydetection in a computed tomography (CT) device. The array can be aone-dimensional string or a two-dimensional (2D) array. CT devices canbe used in a variety of applications, including medical imaging,industrial imaging, nondestructive testing, imaging subsurface minerals,and various other uses. Because the sensor modules are positionedadjacent one another in the array in some implementations, the sensor,the processor, and other components must fit within their associatedarea in the array. Moreover, because there are neighboring sensormodules on each side of a particular sensor module, it is important todesign transmission elements connecting the sensor module to theexternal control module so that they do not interfere with neighboringsensor modules. In other imaging applications, sensor modules can beused to detect sound waves within an ultrasound system. In yet otherimplementations, sensor modules can be employed in nuclear imagingapplications, such as in positron emission tomography (PET) scans andgamma ray imaging applications. In nuclear imaging applications, asensor (or sensor array in some embodiments) can be used to image anobject (e.g., a patient) that has been provided with (e.g., ingested orbeen injected with) a radioactive tracer material.

Accordingly, it can be advantageous to provide a compact sensor modulethat positions the sensor close to processing electronics while ensuringthat the sensor and/or sensor substrate is sufficiently insulated fromheat generated by the processing electronics.

SUMMARY OF THE INVENTION

In one embodiment, a sensor module is disclosed. The sensor module cancomprise a sensor substrate and a sensor die mounted on the sensorsubstrate. The sensor module can further comprise a flexible processorsubstrate having a mounting portion and at least one end portionextending from the mounting portion. A processor die can be mounted onthe mounting portion of the flexible processor substrate. A thermallyinsulating stiffener can be disposed between the sensor substrate andthe mounting portion of the flexible processor substrate. The endportion of the flexible processor substrate can be bent around an edgeof the stiffener to electrically couple to the sensor substrate.

In another embodiment, a method for forming a sensor module isdisclosed. The method can comprise providing a sensor substrate, aflexible processor substrate, and a thermally insulating stiffenerhaving a first side and a second side opposite the first side. Themethod can further include mounting a sensor die to the sensor substrateand mounting a processor die to the flexible processor substrate. Inaddition, the method can comprise attaching the flexible processorsubstrate to the second side of the stiffener. A first end portion ofthe flexible processor substrate can be bent at an edge of thestiffener. The method can also comprise electrically coupling the firstend portion of the flexible processor substrate to the sensor substrate.The first side of the stiffener can face the sensor substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of an array of sensor modules for a CT deviceaccording to one embodiment.

FIG. 2 is a perspective view of an assembled sensor module according toone embodiment.

FIG. 3 is an exploded isometric view of the sensor module of FIG. 2.

FIG. 4 is a side cross-sectional view of the assembled sensor module ofFIG. 2.

FIG. 4A is an enlarged cross-sectional view of a portion of the sensormodule illustrated in FIG. 4.

FIG. 5 is a top perspective view of a stiffener according to oneembodiment.

FIG. 6 is a top perspective view of a radiation shield attached to thestiffener of FIG. 5 according to one embodiment.

FIG. 7 is a bottom perspective view of the stiffener according to oneembodiment.

FIG. 8 is a bottom perspective view of a flexible processor substrate,multiple processor dies, and a connector, according to one embodiment.

FIG. 9 is a top perspective view of multiple passive electroniccomponents mounted on the flexible processor substrate, according to oneembodiment.

FIG. 10 is a side cross-sectional view of a heat spreader, an electronicconnector, and a finned heat sink extending from the heat spreader.

FIG. 11 is a top perspective view of an assembled sensor moduleaccording to another embodiment.

FIG. 12 is an exploded isometric view of the assembled sensor module ofFIG. 11.

FIG. 13 is a side cross-sectional view of the assembled sensor module ofFIG. 11.

FIG. 13A is an enlarged cross-sectional view of a portion of the sensormodule illustrated in FIG. 13.

FIG. 14 is a top perspective view of a stiffener according to oneembodiment.

FIG. 15 is a top perspective view of a radiation shield attached to thestiffener of FIG. 14.

FIG. 16 is a bottom perspective view of the stiffener according to oneembodiment.

FIG. 17 is a bottom perspective view of a flexible processor substrate,multiple processor dies, and a connector, according to one embodiment.

FIG. 18 is a top perspective view of multiple passive electroniccomponents mounted on the flexible processor substrate of FIG. 17.

FIGS. 19A-D are bottom perspective views of various components of asensor module, according to another embodiment.

FIG. 20 is a flowchart illustrating one method for assembling a compactsensor module.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates an imaging system 10 according to one embodiment. Insome implementations, the imaging system 10 can be a CT device. CTdevices are useful in a variety of fields, including medical imaging,industrial imaging, nondestructive testing, and subsurface imaging. Inthe imaging system 10 of FIG. 1, a source 11 can emit radiation 12 inthe direction of an object 13 (e.g., a patient) to be imaged. In oneembodiment, the source 11 emits x-ray radiation. Skilled artisans willunderstand that there are various conventional mechanisms to emitradiation for imaging purposes. After some portion of the radiation 12passes through the object 13, it reaches a one-dimensional (1D) ortwo-dimensional (2D) array of sensor modules 1 positioned opposite thesource 11. The sensor modules 1 can be configured to convert visiblelight to electrical signals using a photodiode array (PDA), which can bethe sensor of this imaging example. In some implementations, the sensormodule 1 may also be configured to convert detected x-ray radiation tovisible light, or the system 10 can include a separate scintillator forthat purpose. The sensor module 1 is also configured to convert theanalog signals received from the PDA into digital signals that can betransmitted by transmission elements 15 to an external control module14. The sensor module 1 can also perform various other preprocessingand/or preconditioning operations on the detected signals beforetransmission to the control module 14. After the processed digitalsignals are received by the control module 14, the control module 14 canfurther process the digital signals into a readable output, such as animage on a display device or a report of various measured valuescalculated from the received signals. To obtain a full 3D image of theobject 13, the system 10 can rotate around the object 13 in thedirection A shown in FIG. 1 to obtain images of the subject 13 atvarious angles.

In other embodiments, the imaging system can be an ultrasound device.Although an ultrasound device is not expressly illustrated herein, itshould be appreciated that an ultrasound device, according to someembodiments, can include a source of ultrasonic waves and a detector (ordetector array) that includes one or more sensor modules similar tothose described in more detail below. Furthermore, the sensor module(s)can be used in nuclear imaging implementations, such as PET scans andgamma ray imaging techniques. In yet other embodiments, the sensormodules can be used in various non-imaging arrangements, e.g.,electrical, electronic, or optical applications that employ a compactmodule that includes both a sensor and a processor. For example,microelectromechanical systems (MEMS) devices, such as MEMS microphonesand accelerometers, may include both a sensor die and a processor dienear the sensor in order to process signals from the sensor. In theseembodiments, sensor modules similar to those illustrated herein may beuseful in providing a compact sensor package, while thermally insulatingthe sensor from the processor.

Turning to FIG. 2, a perspective view of an example sensor module 1 isillustrated. The sensor module 1 can include one or more sensor dies 2mounted on a sensor substrate 3. In some embodiments, the sensor die 2can comprise an x-ray sensing device, including, e.g., a PDA or otherimaging sensor. In x-ray applications, the module may also include acollimator and a scintillator array for converting the x-rays to visiblelight, or the collimator and scintillator can be separately providedover the module within the imaging system. In still other embodiments,the sensor die 2 can include any other suitable device configured todetect signals, including, e.g., MEMS sensors and other electrical andelectronic sensors. Note that, although the sensor module 1 illustratestwo sensor dies 2, in other embodiments, it is possible to only use onesensor die or greater than two sensor dies.

The sensor dies 2 are mounted on a sensor substrate 3. The sensorsubstrate 3 can be any suitable substrate, including a printed circuitboard (PCB) or ceramic substrate. In the illustrated embodiment, thesensor substrate 3 is a flexible substrate with integrated bond pads,leads and traces, which allows for a low profile; however, in otherembodiments, the sensor substrate can be substantially rigid. In variousother embodiments, it is possible to use a leadframe-based substrate forthe sensor substrate 3. The sensor substrate 3 can include multipleconductive leads configured to electrically couple to external devicesor substrates. In some embodiments, the sensor die 2 can be mechanicallyand electrically coupled to the sensor substrate 3 by way of a goldthermocompression bond with an underfill epoxy. In other embodiments,the sensor die 2 can be soldered to the sensor substrate 3, while in yetother embodiments, the sensor die 2 can be coupled to the sensorsubstrate 3 using anisotropic conductive film (ACF) or non-conductivepaste (NCP) technologies.

As noted, the illustrated sensor substrate 3 is a flexible substrate.Flexible substrates can be useful in arrangements where it is desirablefor the substrate to conform to a particular geometry employed within asystem. Flexible substrates can be made of a flexible plastic material,such as polyimide or PEEK and can include integrated bond pads, tracesand leads similar to those used in conventional PCB substratetechnologies. The flexible substrate can be easily bent or folded toconform to a particular geometry. The traces and leads can be patternedon the flexible substrate in very small dimensions. For example, in someembodiments, the traces can have line widths and spaces on the order ofabout 15 to 20 μm, and the leads or bond pads can have widths ordiameters of about 200-300 μm with similar spacing, such that the pitchis on the order of 400-600 μm. By employing small lead pitch, it ispossible for the sensor substrate to electrically communicate with alarge number of pixels (e.g., corresponding to portions of the PDA),which can advantageously increase the resolution of the imaging device.In one embodiment, each sensor die 2 can include 512 pixels electricallycoupled to the sensor substrate 3. In yet other embodiments, the linewidths and spaces can be much smaller or larger, depending on thedesired lead density for a particular arrangement.

Returning to FIG. 2, the sensor substrate 3 can be mounted on or coupledto a portion of a stiffener 4. As will be discussed in more detailbelow, the stiffener 4 can provide structural support for the sensormodule 1. The stiffener 4 can also be made of a thermally insulatingmaterial (such as a plastic or ceramic) to thermally insulate the sensordie 2 and/or sensor substrate 3 from a processor die (not shown in FIG.1). While not shown in FIG. 2, the sensor module 1 can also include aheat spreader 16 (illustrated in FIG. 3) coupled to the stiffener 4. Thesensor module 1 can further comprise a connector 5 that is configured toelectrically connect the sensor module 1 with the external controlmodule 14 (FIG. 1). For example, the connector 5 can include variouselectrical contacts that are configured to electrically communicatesignals received and/or processed within the sensor module 1 to theexternal control module 14. In some embodiments, a cable or othertransmission element (e.g., transmission elements 15) can be used toelectrically connect the connector 5 with the external control module14.

FIG. 3 illustrates a 3D perspective exploded view of various componentsof the sensor module 1. As mentioned above, the sensor module 1 caninclude the sensor die 2 and the sensor substrate 3. The sensor module 1can also include a flexible processor substrate 8, shown in a foldedcondition, and one or more processor dies 9 to be mounted on theflexible processor substrate 8. As will be described in more detailbelow, the flexible processor substrate 8 can include end portions thatare bent at the edges of the stiffener 4 in order to space the dies 9from the sensor substrate 3 while still making electrical contact to thesensor substrate 3. In addition, the sensor module 1 can include aradiation shield 6 coupled to one side of the stiffener 4. One or morepassive electronic components 7 can be coupled to the flexible processorsubstrate 8. In the configuration illustrated in FIG. 3, the flexibleprocessor substrate 8 is folded over the passive electronic components7, the stiffener 4, and the shield 6, such that these components arepositioned within the bent portions of the stiffener 4. Thus, afterassembly (see FIG. 4), these components intervene between the die(s) 9and the sensor substrate 3. The heat spreader 16 can be coupled to thestiffener 4, and the connector 5 can electrically connect to theflexible processor substrate 8 and/or other components by way of anopening 21 within the heat spreader 16. The opening 21 can be a throughhole formed in the heat spreader 16. In some embodiments, the opening 21can also be defined by a gap formed between two independent portions ofthe heat spreader 16, as shown. While FIG. 3 illustrates one exampleimplementation of the sensor module 1, it should be appreciated that theparticular ordering of components may vary in other implementations. Forexample, in some implementations, the shield can be positioned below thestiffener in FIG. 3, e.g., such that the shield is positioned betweenthe stiffener and the flexible processor substrate.

FIG. 4 illustrates a side cross-sectional view of the sensor module 1,and FIG. 4A illustrates an enlarged view of a portion of FIG. 4. Notethat it may be helpful to refer to FIGS. 5-10 for reference toparticular components when viewing FIGS. 4 and 4A. Turning to FIGS. 4-7,the stiffener 4 can be formed of any suitable thermally insulatingmaterial. For example, in some embodiments, the stiffener 4 can beformed of a rigid plastic material. The stiffener 4 can have a first ortop side 26 and a second or bottom side 25 (FIG. 7) opposite the firstside 26. As shown in FIGS. 4, 4A, and 5, the first side 26 can face thesensor substrate 3. The first side 26 of the stiffener 4 can include afirst recess 33 sized and shaped to receive the shield 6 (FIG. 6). Thestiffener 4 can also include a first aperture 23 and a second aperture24. The first and second apertures 23, 24 can be shaped and sized toallow end portions of the flexible processor substrate 8 to pass throughand electrically connect to the sensor substrate 3. In otherarrangements, particularly where the sensor substrate is rigid, theapertures can be omitted in favor of a narrower stiffener, and theflexible processor substrate can bend around outside edges of thestiffener, rather than around internal edges as shown. The stiffener 4can provide structural support for other components of the sensor module1 and can also provide thermal insulation between the processor die 9and the sensor die 2 and sensor substrate 3.

As shown in FIGS. 4, 4A, and 6, the shield 6 can be attached to thefirst side 26 of the stiffener 4. In some embodiments, the shield 6 canbe housed within the first recess 33 formed in the first side 26 of thestiffener 4, so that the shield 6 is positioned between the stiffener 4and the sensor substrate 3; in other arrangements, the shield can bepositioned between the stiffener and the flexible processor substrate.The shield 6 can be a radiation shield configured to shield theprocessor die 9 from radiation impinging on the sensor module 1. Forexample, in embodiments that detect x-ray radiation, such as in CTdevices, the shield 6 can shield the processor die 9 from x-rayradiation that may damage components in the processor or that otherwisemay disrupt the operation of the processor die 9. In some embodiments, atungsten (W) shield can be used to shield the processor die 9 from strayx-ray radiation received by the sensor die 2. In other embodiments,however, there may be no need for a shield, such as in embodiments thatare not configured to sense x-ray radiation, e.g., an ultrasound device.In some implementations, the shield 6 can be attached to the first side26 of the stiffener 4 using an adhesive material. In yet otherembodiments, the shield can be positioned on the second side 25 of thestiffener 4.

FIG. 7 generally illustrates the second or bottom side 25 of thestiffener 4. The second side 25 of the stiffener 4 can include a secondrecess 20 formed in a relatively large area of the stiffener 4. One ormore third recesses 22 can also be formed in the second side 25 of thestiffener 4. As illustrated in FIGS. 4A and 7, the third recess(es) 22can be formed within the second recess 20. The third recess(es) 22 canbe deeper than the second recess 20, but the third recess 22 can also beformed over an area that is smaller than the area over which the secondrecess 20 is formed. As will be appreciated below, the third recess(es)22 can be shaped and sized to receive or accommodate the passiveelectronic components 7 (FIGS. 3-4A) attached to the flexible processorsubstrate 8. The second recess 20, in turn, can be shaped and sized toreceive or accommodate the flexible processor substrate 8 and theprocessor die 9. In the assembly, the second recess 20 and the thirdrecess 22 can be filled with air, which can act as a thermal insulatorseparating the processor die 9 and the sensor die 2.

Turning to FIGS. 4, 4A, 8, and 9, the flexible processor substrate 8,the processor die(s) 9, the passive electronic components 7, and theconnector 5 are illustrated. At least one end of the processor substrate8 is flexible such that it can be bent to conform to a desired geometry.The flexible processor substrate 8 can be made of a plastic material andcan include multiple electrically conductive leads (not shown)configured to electrically couple to device dies and/or othersubstrates, as discussed above. The flexible processor substrate 8 shownin FIGS. 8 and 9 can include a central mounting portion 27, and a firstend portion 18 and a second end portion 19 that extend from the centralmounting portion 27.

While the illustrated flexible processor substrate has two end portionsbent and electrically connected to the sensor substrate, in someembodiments, only one end portion can be bent around an edge of thestiffener and electrically connected to the sensor substrate. Forexample, FIGS. 8 and 9 illustrate four dies and two end portions foldedaround edges of the stiffener. In one implementation of FIGS. 8 and 9,e.g., the four dies can be mounted on one or two flexible processorsubstrates. In one embodiment, each of the two end portions isconfigured to electrically couple to 256 channels from the sensor and/orsensor substrate, for a total of 512 channels. In other embodiments,however, there may be only one or two dies, or fewer pin outs from thesensor die(s), and sufficient electrical connections can be made viaonly one end portion of the flexible substrate. For example, in someembodiments there may be only one or two processor dies mounted on oneflexible processor substrate. In this case, only one end portion can bebent around an edge of the stiffener to electrically couple to thesensor substrate. In one implementation, the end portion can beconfigured to electrically couple to 256 channels. A skilled artisanwould understand that various other electrical configurations arepossible.

The central mounting portion 27, as referred to herein, can include padsand surfaces configured for mounting device dies, passive electroniccomponents, and other electrical or electronic components. For example,as shown in FIGS. 8 and 9, the central mounting portion 27 of theflexible processor substrate 8 can include a first or top surface 29 anda second or bottom surface 30 opposite the first surface 29. As shown inFIG. 4, the first surface 29 can face the stiffener 4. The first surface29 and the second surface 30 can both include leads or pads that can beused to electrically connect to dies and/or other electrical components.For example, as illustrated, the processor die(s) 9 can be electricallycoupled to the second surface 30 of the central mounting portion 27. Theprocessor die(s) 9 can be mounted to the flexible processor substrate 8using a gold thermocompression bond with underfill epoxy. In otherembodiments, the processor die 9 can be soldered to the flexibleprocessor substrate 8, while in yet other embodiments, the processor die9 can be coupled to the flexible processor substrate 8 using anisotropicconductive film (ACF) or non-conductive paste (NCP) technologies. Thepassive electronic components 7 can be mounted on the first surface 29of the central mounting portion 27, using any suitable technique(including those used for coupling the processor die 9 to the centralmounting portion 27). In some embodiments, the passive electroniccomponents 7 can include, e.g., capacitors that can be used to improvethe operation of the processor die 9. Other passive electroniccomponents 7 can include resistors, inductors, and any other suitablecomponents.

While the processor die 9 and the passive electronic components 7 havebeen illustrated as being mounted on opposing surfaces of the flexibleprocessor substrate 8, it should be appreciated that the passiveelectronic components 7 can be mounted on the same surface as theprocessor die. For example, the passive electronic components 7 and theprocessor die 9 can both be mounted on the first surface 29 of thecentral mounting portion 27, or they can both be mounted on the secondsurface 30 of the central mounting portion 27. In other embodiments, thepassive electronic components 7 can be mounted on the second surface 30,while the processor die 9 can be mounted on the first surface 29. Thoughfour processor dies 9 are illustrated in FIGS. 8-9, it should beappreciated that any number of processor dies 9 can be used, includingone, two, three or more dies. Moreover, while the processor die(s) 9 andthe passive electronic components 7 have been mounted on the centralmounting portion 27, it should be appreciated that components can alsobe formed on the other portions of the flexible processor substrate 8.Indeed, one advantage of using flexible substrate technology is thatleads and internal conductive traces can still function even when thesubstrate is bent to conform to a desired geometry.

Returning to the embodiment illustrated in FIGS. 4 and 4A, the centralmounting portion 27 of the flexible processor substrate 8 can be mountedto the second side 25 of the stiffener 4 using an adhesive, such as athermally cured adhesive. In some embodiments, the central mountingportion 27 can be positioned within the second recess 20 formed in thesecond side 25 of the stiffener 4. A vacuum lamination process can beused in some implementations to attach the central mounting portion 27to the stiffener 4. The thermally insulating stiffener 4 can thereforebe disposed between the sensor substrate 3 and the central mountingportion 27 of the flexible processor substrate 8. The passive electroniccomponents 7 can be housed within the third recess 22, which can remainfilled with air or other thermally insulting material. Also, as shown,the processor die(s) 9, coupled to the second surface 30 of the centralmounting portion 27, can be housed within the second recess 20 formed inthe second side 25 of the stiffener 4. Air (or another thermallyinsulating material) can also fill the remainder of the second recess20. In addition, in other implementations, a potting epoxy compound canbe applied within the second recess 20 and/or the third recess 22. Thepotting epoxy can passivate the die(s) and can aid in securing thecomponents housed within the recesses 20, 22.

In addition, as shown in FIGS. 4, 4A, 8, and 9, the first end portion 18and the second end portion 19 of the flexible processor substrate 8 canbe bent around the stiffener 4 to electrically couple to the sensorsubstrate 3. The first end portion 18 can be bent through the firstaperture 23, while the second end portion 19 can be bent through thesecond aperture 24 formed in the stiffener 4. Note that in otherembodiments, however, there may be no need for apertures 23, 24 in thestiffener 4. For example, in some embodiments, the first and second endportions 18, 19 can instead be bent around outer edges of the stiffener4, rather than bent through apertures within the stiffener 4. Inaddition, in other embodiments, only one end portion may be bent aroundan edge of the stiffener, e.g., an outer edge or an internal edge of anaperture.

As shown in FIGS. 4 and 4A, the first end portion 18 and the second endportion 19 of the flexible processor substrate 8 can be folded over atleast part of the first or top side 26 of the stiffener 4 and/or part ofthe shield 6. In some embodiments, the first end portion 18 and thesecond end portion 19 can attach to the first side 26 of the stiffener 4and/or the shield 6 using a vacuum lamination process. In someimplementations, a thermally cured adhesive can be used to mechanicallycouple the end portions 18, 19 to the stiffener 4 and/or the shield 6.The first and second end portions 18, 19 of the flexible processorsubstrate 8 electrically connect to the sensor substrate 3. In someembodiments, leads from the first and second end portions 18, 19 can besoldered to corresponding leads in the sensor substrate 3. In otherembodiments, leads from the first and second end portions 18, 19 canelectrically connect to corresponding leads in the sensor substrate 3using non-conductive paste (NCP) or anisotropic conductive film (ACF)bonding technologies.

The first and second end portions 18, 19 can thereby provide electricalcommunication between the sensor die 2 (by way of the sensor substrate3) and the processor die 9, by way of internal conductive tracesconnecting the pads on the first and second end portions 18, 19 with thecentral mounting portion 27 of the flexible processor substrate 8. Theprocessor die 9 can therefore receive signals from the sensor die 2 andprocess them, e.g., convert analog signals into digital signals that canbe transmitted to the external control module 14. The processor die 9can also or alternatively perform other preprocessing or conditioningfunctions on the signal before transmission to the external controlmodule 14. Because the processor die 9 is positioned near the sensor die9, parasitic transmission losses can be minimized or substantiallyeliminated. For example, instead of transmitting analog signals from thesensor die 2 to the external control module 14 (FIG. 1), which can belocated far away from the sensor die 2, the detected analog signals canbe routed from the sensor die 2 to conductive traces within the sensorsubstrate 3. The signal can then couple to leads formed in the firstand/or second end portions 18, 19 of the flexible processor substrate 8,which can then route the signal to the processor die 9 using traceswithin the flexible processor substrate 8. After analog-to-digitalconversion, the processed digital signal can be transmitted, withminimal or no losses, a greater distance to the external control module14 by way of the connector 5 and the transmission elements 15.

As mentioned above, while the proximity of the processor die 9 to thesensor die 2 can be advantageous for signal processing, the heatgenerated by the processor die 9 (and/or other associated electrical orelectronic components) can damage the sensor die 2 if the heat iseffectively conducted to the sensor die 2 and/or the sensor substrate 3.As shown in FIGS. 4 and 10, one way to conduct heat away from theprocessor die 9 and the sensor die 2 is to couple the heat spreader 16to the second side of the stiffener 4. Note that while the heat spreader16 of FIGS. 4 and 10 is illustrated as a substantially planar plate thatcouples to walls of the stiffener 4, in other embodiments, the heatspreader 16 can include walls extending into the sensor module 1 tocouple to a recess or edge of the stiffener 4 (or other suitablestructural component). The heat spreader 16 can be any suitable thermalconductor, such as a metal. The heat spreader 16 is positioned adjacentthe processor die 9, which can enhance thermal conduction between theprocessor die 9 and the heat spreader 16. The processor die 9 cantherefore be positioned between the heat spreader 16 and the stiffener4. Furthermore, in some embodiments, thermal grease or another thermallyconductive filler material can be applied within the gap between theprocessor die 9 and the heat spreader 16 to improve thermal conductionaway from the processor die 9 and away from the sensor die(s) 2. In someembodiments, a heat sink 31 (FIG. 10) can be mounted on the heatspreader 16 to enhance conduction away from the processor die 9 and thesensor die 2. The heat sink 31 can include a plurality of fins 32 thatincrease the surface area of the heat sink 31 to allow heat to morerapidly dissipate into the air or surrounding environment. In otherembodiments, there may not be a heat sink 31, in which case the thermalenergy is allowed to dissipate directly into the air from the heatspreader 16. While the heat sink 31 can be formed as a separatecomponent from the heat spreader 16, it should be appreciated that theheat spreader 16 can be integrated with the heat sink 31 such that anintegrated heat sink/spreader is coupled to the second or bottom side 25of the stiffener 4.

The embodiment of FIGS. 2-10 allows the processor die 9 to electricallycouple to the sensor die 2 over a distance short enough to minimizetransmission losses, while thermally insulating the sensor die 2 (andsensor substrate 3) from heat generated by the processor die 9 that canpotentially damage the sensor die 2 and/or sensor substrate 3. At thesame time, the illustrated module assembly has a very low overallprofile, e.g., a thickness of less than about 10 mm from the sensordie(s) to the heat spreader 16, preferably between about 3 mm and about6 mm. For example, in the illustrated embodiment without the heat sink,the thickness is between about 4 mm and about 5 mm, particularly about4.6 mm. As shown best in FIG. 4, in one embodiment, one or morethermally insulating components can separate the processor die 9 fromthe sensor substrate 3 and the sensor die 2. For example, the thermallyinsulating stiffener 4 is positioned between the processor die 9 and thesensor substrate 3, which can effectively impede heat transfer to thesensor substrate 3 and sensor die 2. Moreover, the air (or otherthermally insulating material in some embodiments) filling the secondrecess 20 and the third recess 22 can assist in thermally insulating theprocessor die 9 from the sensor die 2 and the sensor substrate 3. And,even though the flexible processor substrate 8 and the shield 6 mayinclude conductive components, these components nevertheless physicallyseparate the processor die 9 from the sensor die 2 and the sensorsubstrate 3. Therefore, by being positioned between the processor die 9and the sensor substrate 3 (and the sensor die 2), the thermallyinsulating stiffener 4 and the air or other insulating material cansubstantially inhibit the flow of thermal energy (e.g., heat flow) fromthe processor die 9 to the sensor die 2 and/or the sensor substrate 3.

In addition to the thermally insulating components separating theprocessor die 9 from the sensor die 2 and/or the sensor substrate 3, thesensor module 1 can also include thermally conductive components on theother side of the processor die 9. The thermally conductive componentscan enhance the transfer of thermal energy away from sensor die 2 andthe sensor substrate 3, and toward the heat sink 31 (or directly to thesurrounding environment in embodiments without a heat sink). Forexample, the thermally conductive heat spreader 16 in the illustratedembodiments can be positioned adjacent the processor die 9 and cantherefore effectively conduct heat from the processor die 16 in adirection away from the sensor die 2 and the sensor substrate 3.Moreover, in some embodiments, thermally conductive grease or otherconductive filler material can be applied between the processor die 9and the heat spreader 16, and/or in gaps between the heat spreader 16and the flexible processor substrate 8. The thermally conductive fillermaterial can assist in transferring heat away from the processor die 9and toward the heat spreader 16. Consequently, in some embodiments, theconductive heat spreader 16 and/or the conductive filler material canconduct heat away from the sensor die 2, while the insulating materials(e.g., the stiffener 4 and the air gaps formed in recesses 20, 22) canimpede the flow of heat in the direction of the sensor die 2 and sensorsubstrate 3. Thus, the disclosed configuration can create a thermalpathway that ensures that most of the heat generated by the processordie 9 will be transferred away from the sensor 2 and/or sensor substrate3. However, it should be appreciated that in some embodiments, thestiffener 4 alone can provide sufficient thermal insulation to thermallyseparate the processor die 9 from the sensor die 2 and the sensorsubstrate 3.

FIGS. 11-18 illustrate another embodiment of the sensor module 1. Ingeneral, like reference numerals denote parts similar to those disclosedin FIGS. 1-10. In addition, some of the structure of the sensor moduledisclosed in FIGS. 11-18 can be the same as those in FIGS. 1-10, exceptwhere noted herein. For example, unlike in FIGS. 1-10, the first andsecond end portions 18, 19 of the flexible processor substrate 8 are notfolded over the first side 26 of the stiffener 4 in the embodiments ofFIG. 11-18. Instead, as illustrated in FIGS. 12, 13, and 17-18, thefirst and second end portions 18, 19 of the flexible processor substrate8 are bent at an edge of the stiffener 4 (e.g., an internal edge atfirst and second apertures 23, 24) and electrically couple to the sensorsubstrate 3 without folding over the first side 26 of the stiffener 4.Even though the configuration of FIGS. 11-18 are different from those ofFIGS. 2-10, the illustrated embodiments can likewise improve signalprocessing by locating the processor die 9 near the sensor die 2 andproviding a very low overall profile, while thermally insulating theprocessor die 9 from the sensor die 2 and/or the sensor substrate 3.

FIGS. 19A-D illustrate another embodiment of various components of asensor module 1. As above, like reference numerals denote parts similarto those disclosed in FIGS. 1-18. Unlike the single flexible processorsubstrate 8 illustrated in, e.g., FIG. 3, FIG. 19A illustrates anembodiment having two flexible processor substrates 8 separated withinthe stiffener 4. While only two flexible processor substrates 8 areillustrated in FIG. 19A, it should be appreciated that more than twoflexible processor substrates 8 (e.g., 3, 4, or more) may be providedwithin the sensor module 1.

Furthermore, as shown in FIG. 19B, a pigtail connector 57 can be used toelectrically connect the sensor module 1 to the external control module14 (or other external systems). The pigtail connector 57 of FIG. 19B,for example, is mechanically and electrically coupled to the flexibleprocessor substrates 8 using any suitable technique. For example, thepigtail connector 57 can be soldered to the flexible processorsubstrates 8, or the pigtail connector can be coupled to the flexibleprocessor substrates 8 using NCP or ACF technologies, as discussedabove. As shown in FIG. 19B, the pigtail connector 57 can be mounted tospan and electrically connect to both flexible processor substrates 8and can exit the stiffener 4 at a first outer edge 58 of the stiffener4.

FIGS. 19C and 19D illustrate various implementations of the heatspreader 16 and the heat sink 31. In FIG. 19C, a finned heat sink 31having multiple fins 32 is coupled to the second or bottom side 25 ofthe stiffener 4. In FIG. 19D, a heat spreader 16 is shown coupled to thestiffener 4 without a heat sink. As mentioned above, the heat spreader16 can be integrated with the heat sink 31 to form a single component,or the heat spreader 16 can be formed as a separate component from theheat sink 31. In the illustrated embodiments of FIGS. 19C and 19D, thepigtail connector 57 extends from the first outer edge 58 of thestiffener 4 and extends away from the sensor module 1 in a direction 61parallel to the thickness of the module 1. Unlike the connector 5 (whichis illustrated as being mounted through an opening in the center of theheat spreader and/or heat sink), therefore, the pigtail connector 57 canbe oriented out of the path that conducts heat away from the processorand sensor dies. The configuration of FIGS. 19A-D can thereby furtherimprove the thermal properties of the sensor module 1.

Turning to FIG. 20, one method 40 for forming a compact sensor module isshown. The skilled artisan will readily appreciate that the steps neednot be performed in the sequence illustrated. In Block 42, a sensorsubstrate, a flexible processor substrate, and a thermally insulatingstiffener are provided. The sensor substrate can be any suitable sensorsubstrate, including a PCB or ceramic substrate. The sensor substratecan also be formed of a flexible substrate material to reduce moduleprofile relative to, e.g., use of PCB. The flexible processor substrateis a flexible substrate and can have multiple electrical leadsconfigured to electrically couple to device dies and/or othersubstrates. The stiffener can be, e.g., a plastic stiffener having afirst side and a second side opposite the first side.

A sensor die can be mounted to the sensor substrate in Block 44. Asabove, the sensor die can be any suitable sensor die, including, e.g.,an x-ray sensing device that may further include a photo detector array(PDA) or other imaging sensor. In other embodiments, the sensor die 2can include any other suitable device configured to detect signals,including, e.g., MEMS sensors and other electrical and electronicsensors. Moreover, the sensor die can be mechanically and electricallycoupled to the sensor substrate by way of a gold thermocompression bondwith an underfill epoxy, or by using NCP or ACF bonding technologies.

Turning to Block 46, a processor die is mounted to the flexibleprocessor substrate. The processor die can comprise a general processoror an Application-Specific Integrated Circuit (ASIC) processor. Aparticular example includes an analog-to-digital converter (ADC). Theprocessor die can be bonded to the flexible processor substrate by anysuitable mechanism, including the thermocompression, ACF, and NCPbonding technologies mentioned above.

In Block 48, the flexible processor substrate is attached to the secondside of the stiffener. As described in detail above, a central mountingportion of the flexible processor substrate can be attached to thesecond side of the stiffener, such as within a recess formed in thesecond side of the stiffener. The flexible processor substrate can beattached to the stiffener in any suitable manner, including using athermally curable adhesive material.

In Block 50, at least one of first and second end portions of theflexible process substrate can be bent around the edges of thestiffener. As described above, the first and second end portions canextend from the central mounting portion. In some implementations, thefirst and second end portions can be bent around outer edges of thestiffener. In other embodiments, however, the first and second endportions can be bent around internal edges of the stiffener, e.g.,through first and second apertures formed through the stiffener. Thefirst and second end portions can be further folded over the first sideof the stiffener.

At least one of the first and second end portions of the flexibleprocessor substrate can be electrically coupled to the sensor substratein Block 52. The first side of the stiffener can face the sensorsubstrate. In some embodiments, one or both of the first and second endportions can be soldered to the sensor substrate, while in otherembodiments, ACF or NCP technologies can be used to electrically connectthe flexible processor substrate to the sensor substrate. Additionally,where fewer connections are needed, electrical connections can be madeexclusively at one of the end portions, and the other end portion neednot be bent around an edge of the stiffener.

Furthermore, a radiation shield can be mounted to the first side of thestiffener between the stiffener and the sensor substrate in someembodiments. For example, the shield can be mounted within a recessformed in the first or top side of the stiffener, nearest to the sensordie(s). The shield can be bonded to the stiffener using an adhesive insome implementations. Moreover, the sensor substrate can also beattached to the shield and/or to the first side of the stiffener usingan adhesive or other bonding technique. To enhance heat transfer awayfrom the sensor die, a heat spreader can be attached to the second orbottom side of the stiffener adjacent the processor die. The processordie can therefore be positioned between the stiffener and the heatspreader. To enhance thermal conductivity between the processor die andthe heat spreader, a thermally conductive grease or filler material canbe applied between the processor die and the heat spreader. In addition,a connector can be electrically coupled to the flexible processorsubstrate through an opening in the heat spreader. The connector canprovide electrical communication between the sensor module and anexternal control module. Further, passive electrical components, such ascapacitors, can be electrically coupled to the flexible processorsubstrate to assist the processor in processing the detected signals.While certain steps of the method 40 have been presented in a particularorder, it should be appreciated that the steps can be performed in anyother suitable order.

Although this invention has been disclosed in the context of certainembodiments and examples, it will be understood by those skilled in theart that the present invention extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses of theinvention and obvious modifications and equivalents thereof. Inaddition, while several variations of the invention have been shown anddescribed in detail, other modifications, which are within the scope ofthis invention, will be readily apparent to those of skill in the artbased upon this disclosure. It is also contemplated that variouscombinations or sub-combinations of the specific features and aspects ofthe embodiments may be made and still fall within the scope of theinvention. It should be understood that various features and aspects ofthe disclosed embodiments can be combined with, or substituted for, oneanother in order to form varying modes of the disclosed invention. Thus,it is intended that the scope of the present invention herein disclosedshould not be limited by the particular disclosed embodiments describedabove, but should be determined only by a fair reading of the claimsthat follow.

What is claimed is:
 1. A sensor module comprising: a first substrate anda second substrate; a sensor die in electrical communication with thefirst substrate and the second substrate; a processor die in electricalcommunication with the first substrate and the second substrate; and astiffener having a first side and a second side opposite the first side,wherein the first and second sides of the stiffener include majorsurfaces of the stiffener, the stiffener disposed between the sensor dieand the processor die such that the first side faces the sensor die anda first normal line passes perpendicularly through the major surface ofthe first side and intercepts the sensor die, and such that the secondside faces the processor die and a second normal line passesperpendicularly through the major surface of the second side andintercepts the processor die, wherein one of the first and secondsubstrates includes a bent portion and a mounting portion extending fromthe bent portion, the bent portion folded around an edge of thestiffener to electrically couple the sensor die and the processor die,and wherein the processor die is directly mounted to one of the firstand second substrates and the sensor die is mounted over the other ofthe first and second substrates, and wherein the stiffener is furtherdisposed between a first portion of the first substrate and a secondportion of the second substrate, such that the first normal lineintercepts one of the first portion and the second portion and thesecond normal line intercepts the other of the first portion and thesecond portion.
 2. The sensor module of claim 1, wherein the secondsubstrate includes the bent portion and the mounting portion, whereinthe processor die is mounted to the mounting portion of the secondsubstrate, and wherein an end portion of the second substrate extendsfrom the bent portion opposite the stiffener from the mounting portionto electrically connect to the first substrate.
 3. The sensor module ofclaim 2, wherein the mounting portion of the second substrate is coupledto the second side of the stiffener.
 4. The sensor module of claim 3,wherein the mounting portion of the second substrate has a first surfacefacing the stiffener and a second surface opposite the first surface,and wherein the processor die is mounted on the second surface of themounting portion.
 5. The sensor module of claim 4, further comprising aplurality of passive electrical components electrically coupled to thefirst surface of the mounting portion of the second substrate andpositioned within at least one recess formed in the second side of thestiffener.
 6. The sensor module of claim 1, wherein the second substrateincludes the bent portion and the mounting portion, and wherein firstand second opposite end portions of the second substrate bend aroundedges of the stiffener to electrically connect to the first substrate.7. The sensor module of claim 1, wherein the second substrate includesthe bent portion and the mounting portion, and wherein a first endportion of the second substrate is bent through a first aperture formedin the stiffener to electrically communicate with the first substrate.8. The sensor module of claim 7, wherein the first end portion is foldedover at least part of the first side of the stiffener.
 9. The sensormodule of claim 1, further comprising a radiation shield coupled withthe first side of the stiffener.
 10. The sensor module of claim 9,wherein the radiation shield is housed within a recess formed in thefirst side of the stiffener.
 11. The sensor module of claim 1, whereinthe sensor die comprises an image sensor die.
 12. The sensor module ofclaim 11, wherein the sensor die comprises a photodiode array.
 13. Animaging device comprising an array of multiple sensor modules, eachsensor module in the array comprising the sensor module of claim
 1. 14.The imaging device of claim 13, wherein the imaging device is a CTdevice.
 15. A sensor module comprising: a first substrate and a secondsubstrate; a sensor die in electrical communication with the firstsubstrate and the second substrate; a processor die in electricalcommunication with the first substrate and the second substrate; and astiffener having a first side and a second side opposite the first side,wherein one of the first and second substrates includes a bent portionand a mounting portion extending from the bent portion, the bent portionfolded around an edge of the stiffener to electrically couple the sensordie and the processor die, wherein a first segment of one of the firstand second substrates is disposed along the first side of the stiffenerand a second segment of one of the first and second substrates isdisposed along the second side of the stiffener, wherein the processordie is directly mounted to one of the first and second substrates andthe sensor die is mounted over the other of the first and secondsubstrates, and wherein the stiffener is further disposed between afirst portion of the first substrate and a second portion of the secondsubstrate, such that the first portion includes one of the first segmentand the second segment and the second portion includes the other of thefirst segment and the second segment.
 16. The sensor module of claim 15,wherein the second substrate includes the bent portion and the mountingportion, wherein the processor die is mounted to the mounting portion ofthe second substrate, and wherein an end portion of the second substratethat extends from the mounting portion is bent around the edge of thestiffener to electrically connect to the first substrate.
 17. The sensormodule of claim 16, wherein the stiffener is disposed between the firstsubstrate and the mounting portion of the second substrate.
 18. Thesensor module of claim 17, wherein the first and second sides of thestiffener include major surfaces of the stiffener, the stiffenerdisposed between the first substrate and the mounting portion of thesecond substrate such that the first side faces the first substrate anda first normal line passes perpendicularly through the major surface ofthe first side and intercepts the first substrate, and such that thesecond side faces the mounting portion of the second substrate and asecond normal line passes perpendicularly through the major surface ofthe second side and intercepts the mounting portion of the secondsubstrate.
 19. A sensor module comprising: a first substrate and asecond substrate; a sensor die in electrical communication with thefirst and second substrates; a processor die in electrical communicationwith the first and second substrates; and a stiffener having a firstside including a recess formed therein and a second side opposite thefirst side, wherein one of the first and second substrates is bentaround an edge of the stiffener to electrically couple the sensor dieand the processor die, wherein a first segment of one of the first andsecond substrates is disposed along the first side of the stiffener anda second segment of one of the first and second substrates is disposedalong the second side of the stiffener, wherein the stiffener is furtherdisposed between a first portion of the first substrate and a secondportion of the second substrate; and a radiation shield disposed in therecess of the first side of the stiffener.